1. Technical Field
The present disclosure generally relates to a liquid crystal display device, and more particularly to a liquid crystal display device including a spacer that has at least two surfaces with different horizontal plane, thereby resulting in a two-stage deformation.
2. Description of the Related Art
A liquid crystal display (LCD) device typically includes a pair of substrates that are maintained in a space apart, yet parallel relationship with each other. The space between the substrates is commonly referred to as the cell gap. Interposed between the substrates, within the cell gap, is a liquid crystal material that changes its optical characteristics in response to an applied electrical signal.
In order to assure the proper operation of a liquid crystal display device, it is critical that the cell gap is maintained uniformly and precisely throughout the entire display. For example, even slight deviations in the cell gap will result in a noticeable and defective appearance in the display (so-called chrominance non-uniformity or Mura defect). This can readily be seen in a conventional LCD display panel with a fingertip pressure on the surface. In response to the pressure, the cell gap in the affected area will be reduced slightly, resulting in a dark spot, degradation of contrast or other undesirable defects in the displayed image.
In a conventional technology, the LCD device includes a thin film transistor (TFT) substrate 61, a color filter substrate 71 and a liquid crystal material 69 sandwiched therebetween, shown in FIG. 1. The cell gap is maintained by providing a plurality of spacers 79 between the two substrates 61, 71. The spacers 79 which are of a uniform height are disposed randomly within the cell gap by generally utilizing a spraying technique. This generally causes the non-uniform distribution of the spacers partial density. To ensure that an adequate density of spacers to maintain the proper cell gap is disposed in all areas of the display, a superfluity of spacers must be used. In addition, according to such conventional techniques for placement of the spacers, they are placed in both “inactive” and “active” areas of the display. The “active” areas are those areas where the liquid crystal material may be selectively activated because they are located between two opposite electrodes on the substrates. The “inactive” areas are those areas where the liquid crystal material cannot be selectively activated because of the absence of the opposite electrodes on the substrates.
U.S. Pat. No. 4,653,864, entitled “Liquid Crystal Matrix Display Having Improved Spacers And Method Of Make Same,” discloses a liquid crystal display 2 incorporated herein by reference, shown in FIG. 2. The liquid crystal display 2 includes a first substrate 10; a plurality of first pixel electrodes 12 disposed on the first substrate 10; a plurality of isolation devices 14 and address lines 16 disposed on the first substrate 10; a second substrate 20; a plurality of second pixel electrodes 13 disposed on the second substrate 20; light influencing display material 15 between the first and second substrates 10, 20; and spacer means 8 for spacing the first and second substrates 10, 20 apart, wherein the spacer means 8 is disposed on the second substrate 20 and includes a plurality of discrete bodies 8a, 8b arranged in a predetermined pattern.
U.S. Pat. No. 6,108,068, entitled “Liquid Crystal Display Apparatus Using Spacers Having Double Structure,” discloses a liquid crystal display 30 incorporated herein by reference, shown in FIG. 3. The liquid crystal display 30 includes a liquid crystal layer 32 sandwiched by a front glass substrate 40 and a back glass substrate 50, wherein the liquid crystal layer 32 is provided with a plurality of spacers 38 to maintain a predetermined thickness of the liquid crystal layer. The spacer 38 has a double structure consisting of an elastic external portion 36 and a kernel portion 34. The kernel portion 34 is made of a material that is higher than that of the elastic external portion 36 in hardness. Also, the external hull portion 36 of the spacer 38 is electrically conductive. However; the liquid crystal display 30 is merely considered enabling to reduce flicker and baking generated by electric charge caused by impurities ions remaining on the boundary surface of the liquid crystal layer.
Recently, a technology for rapidly filling the liquid crystal, i.e. a One Drop Fill (ODF) technology of the liquid crystal, is developed. In this technology, one of two substrates is accommodated with the injected liquid crystal material by dropping, before the two substrates will be joined with each other. The filling method of the liquid crystal is disclosed in U.S. Pat. No. 5,263,888, entitled “Method of Manufacture of Liquid Crystal Display Panel,” issued to Teruhisa Ishihara et al. on Nov. 23, 1993.
According to a manufacturing process of the One Drop Fill (ODF) technology of the liquid crystal, the operation window (or process window) of the quantity of the injected liquid crystal on the substrate depends on the elasticity of the spacer. When the number of the spacers is too few or the plastic deformation of the spacers is too large (e.g. elastic constant is too low), it can be observed that the relative quantity of the liquid crystal is too much so as to result in the gravity mura. When the number of the spacers is too many or the plastic deformation of the spacers is too small (e.g. elastic constant is too high), it can be observed that the relative quantity of the liquid crystal is too little so as to result in air bubbles. In the mode of an ideal elastomer, the spacer with higher height can acquire the larger operation window.
The prior art has been developed for enlarging the operation window of the quantity of the liquid crystal in the manufacturing process of the ODF technology. For example, as shown in FIG. 4, a liquid crystal display device 80 includes a first substrate 90, a second substrate 98 and a plurality of first and second spacers 92, 94. The first and second spacers 92, 94 are substantially of the same height. The first spacers 92 are disposed on the first substrate 90 and contact the elements, such as thin film transistors, which are protrudently located on the second substrate 98. The second spacers 94 are disposed on the first substrate 90 and do not contact the second substrate 98, i.e. there is a gap to be formed between the second spacers 94 and the second substrate 98. According to the above-mentioned arrangement of the spacers, when the first and second substrates 90, 98 are pressed, the first spacers 92 are firstly compressed. Then, when the second substrate 98 further contacts the second spacers 94, the first and second spacers 92, 94 are simultaneously compressed. Thus, the first and second spacers 92, 94 cooperate to form a process with two-stage elastic deformation, thereby enlarging the operation window of the quantity of the liquid crystal in the manufacturing process of the ODF technology. However, such hybrid spacers of the liquid crystal display device have a relatively complex structure.
Accordingly, there exists a need for a liquid crystal display device including a spacer that has a two-stage deformed process for enlarging the operation window of the quantity of the liquid crystal and also has simple structure.